A MILE-A-MINUTE DAY
Rob Manning July 2, 1997: 6:30pm Pacific This has been a mile-a-minute type of day. I'll tell you, the excitement and drama of what's going on is up to a high pitch. Everyone's fingers are clammy! I slept pretty well last night, though I did wake up at 4 a.m. to do some work. I sat in my bathrobe at my dining room table going through all these numbers, looking at the times and getting the idea that yes, this IS going to work! When we run through the software in our testbed we actually can watch all the events that happen. We have support equipment that listens in to what the computer and the hardware are doing, including opening the airbags and rockets (even though there are no real rockets opening). We can make sure that all the events that are supposed to happen, happen and that they are happening at the right instant. We're actually trying to make sure that everything happens to within a fraction of a second of accuracy. When we do one of these tests, it produces a whole ream of paper that unfortunately we have to go through by hand to really understand what's going on. However, every time we run these tests the software causes the rockets to fire within a few thousandths of a second of when they're supposed to fire. This is better than we need, by a lot! It's so much fun to confirm that over and over again! I spent the rest of today answering a lot of fast questions from the media. Our science team did a press conference and all of us were eagerly listening to see how they would handle the bombardment of questions. We're interested to know what kind of questions people have, so we can tune our answers to match the questions. One of the problems we have is that we're so familiar with this mission, we know all the details, that it's hard to really know how much other people know about it. So we basically try to listen to other people's questions and who's doing the asking and then try to judge how to explain all of this. There are a lot of complicated series of events. It's especially hard talking with television reporters because we have to explain things very succinctly and quickly, most importantly very quickly, without using any acronyms and trying to use words that people can see very visually. It takes practice and we're practicing. Tonight, in my free time (which I have very little of!) I'm working on a script that I'm going to read during the landing. I'm trying to synchronize my talking with what I think should be going on at each given moment. I know there's going to be a lot of people listening, all over the world, and I have to make sure I say the right thing and that I don't misplace my tongue. Most importantly, I have to keep my concentration up because I have to get up at 1 a.m. to spend the early morning hours as mission manager for that phase of the descent and landing. Just a few moments ago, we may have sent (we don't know yet for sure) the very last command to the spacecraft until after it lands. We do the best job we can aiming for Mars, but Mars moves! Mars' position is being influenced by Jupiter and the asteroids. Just today we started to see a tug of Mars. Right now Mars looks like the Moon from Earth; that's how big it is if you were on the spacecraft. We are less than a million miles from Mars. And at that distance Mars is starting to pull a little bit and the spacecraft is starting to very slowly accelerate toward Mars, as if it's falling into Mars. Hopefully it falls just the right way so it skims the atmosphere to slow down. It looks like we are a little bit off target, but not too much. We're not going to do to much to change the direction of travel but we want to tell the software onboard exactly where it's going so the spacecraft will open the parachute at just the right height. Even though the software onboard Pathfinder is running and the clocks are ticking, anytime between now and 8:30 a.m., Pacific, Friday, we can send commands to the spacecraft to update these key parameters that control how the parachute gets opened. We have the ability to very quickly generate these commands based on the latest knowledge of where we're going. and that's based on information gathered by our navigators. The Navigation team works together to take our best estimate of where we think we're going and figure out exactly how to take that information and propagate it to the ground. They can actually simulate the spacecraft flying through a computer-generated atmosphere and figure out how the lift and drag work. Pathfinder looks like a funny-shaped glider and we can actually go through the process of simulating that whole lift, drag and acceleration due to gravity (the tug of Mars) all the way down until that point where the parachute opens up and beyond. We do this over and over again with the new information we get. The parachute will open up anywhere from about 5 km above the ground to as high as 11 km or more. In fact it looks like, from where we're coming right now, we're going to open the parachute a little on the high side, which means it'll take a longer time to soar to the ground. The spacecraft is soaring to the ground at a very, very high speed and once the parachute opens it has got a lot to do: get rid of the heat shields, repel down a 20-meter bridle, turn on the radar and start looking for the ground and begin the processing. On top of all of this, Pathfinder has to have enough time to figure out how high it is above the ground and how fast it's going in order to open the airbags. The airbags open about 1000 feet above the ground and once they open, the lander can no longer see the ground through the airbags. That's the reason that we do these updates-to get a better sense of where we're going and to get the parameters just right. The command we sent about 15 minutes ago is still flying through space at this minute. It only takes about 1000 bits of information, which we send from the Deep Space Network in Goldstone, CA. These 1000 bits are shipped up one bit at a time, back-to-back. But even though it takes awhile to get all those bits out the antenna, by the time the last bit is out, the first bit is still flying through space. All those thousand bits are like little soldiers marching in series until they get to Mars, at which time they'll be received one at a time by the spacecraft. My day isn't over yet. Now I must prepare for tomorrow's press conference...
A LONG ROAD NEARING AN END
Linda Robeck-Fuhrman, Deputy Mechanical Engineering Manager for Pathfinder Assembly, Test, and Launch Operations July 2 For Linda, Pathfinder's July 4th landing is the end of a long road begun just over two years ago, when she joined the Pathfinder team for the Assembly Test and Launch Operations phase of the Pathfinder mission. ATLO, as they call it, is where a spacecraft makes its last stop on Planet Earth, first at JPL's Spacecraft Assembly Facility (SAF), and finally at the test and launch facilities at Kennedy Space Center. At KSC, affectionately referred to as "the Cape", the spacecraft goes through final test and assembly, is mated to the launch vehicle for yet another round of testing, and then ultimately lifts off for the trip to Mars. It was just over a year ago that Linda helped pack up Pathfinder to begin its long road to Mars, starting with a four-month intensive effort at the Cape. But even before launch, the events of this hectic week of July 4 1997 were very much in the minds of the entire Pathfinder team. "We were there from June through mid-December, and it was round-the-clock action the entire time." Linda was in charge of the group which assembled and tested the Pathfinder lander. It was a challenging time, since when the inevitable problems came up, Linda's team had to improvise tests and solutions on the spot, far from the support of the main JPL facility in California. "One serious issue that came up was in how the spacecraft would respond to the venting of cooling fluid, which happens right before final approach to the planet on July 4. The concern was that the venting fluid would act as a thruster, either spinning the spacecraft or pushing it off-course. My team had to devise a way to measure the mechanical characteristics of the spacecraft there on-site at the Cape, to prove to ourselves and those back at JPL that the venting could be done without disrupting the spacecraft's motion or attitude." "Another situation we faced, which seems kind of funny now, is when we were doing the final closing of the lander. This lander structure consists of "petals" which fold up around the rover, electronics, and science instruments, and will be opened up again when the lander is safely on Mars. Anyway, this event turned out to be a big public spectacle; Dan Goldin (NASA Administrator) was giving a speech on the same day, and there was a huge crowd of media people and cameras around to witness our buttoning-up of the spacecraft. Well, the petals didn't close all the way. We were horrified! We could see that there was a tiny space between each of the petals, when they were supposed to be sealed tightly. None of the visiting guests could tell, because the gap was small and unless you really knew what to look for you couldn't see it. But we knew that it was supposed to fit perfectly and that something had to be wrong. We had to call off the live video feed into the press conference and send all the press home. Then began the frantic scrambling to find the problem. It turned out that we had never put the whole lander together before with everything on it at one time, and it was now much heavier than it used to be; parts of the lander were sagging under their own weight. The sagging made the parts not quite fit right, which forced us to really look closely at the parts, called "latches" , that held the petals together. It turned out to be serendipitous, because when we really looked at it, we realized we needed some modifications to the latches to make darned sure the thing would work on Mars, even though Mars gravity is much lower than that on Earth. To fix the problem, we actually had people back at JPL pull parts off of an engineering model of the spacecraft, modify them slightly, and then hand-carry them out to the Cape to replace the identical parts we removed from the real spacecraft. It worked out just fine, but it was a desperate few days." Back at JPL, Linda has taught the Pathfinder operations team everything she knows about the lander and how it was put together. She won't be actually involved in the landing activities -- unless something unexpected happens, which means the operations team might be calling her for her expert opinion. "I'm wearing a beeper, and they know they can call me any hour of the day or night. I'll be on pins and needles the whole time, hoping they don't need to." Linda's beeper may also go off this week for an entirely different sort of crisis -- a TV or newspaper crew needs someone to interview, right away! "I'm on the 'Interview List', which means I'll be available at any time to give a commentary on what's going on or to explain something in the mission or spacecraft. Over the last few weeks, they've given us training on how to deal with the media, the kinds of angles that reporters would like to know about, and even what to wear for TV! What's funny is that I've actually heard from a few high school friends of mine, who are now in the news business and are calling me to use the personal touch to get the inside story." "I'm planning to be at JPL for the whole series of events this week -- no, no Fourth of July vacation, but we'll still be celebrating. I'm going to watch the launch events with the rest of my crew from ATLO. These people include guys from the machine shop, technicians, and engineers. We've got a little conference room at the Lab with a TV monitor, a microwave -- we're even getting a fire permit for a BBQ pit right outside! The first spacecraft activity I'll be watching for closely will be that coolant venting event we worried about way back during ATLO. This will happen about 9 in the morning of the 4th. Pretty soon after that, data coming back from the spacecraft will let us know whether things worked out OK. Since it was something I was personally involved in, I'll be anxious to see the results. After that, we won't be able to see much during the descent to the planet surface, so we won't know for sure everything worked until sometime later in the afternoon. We'll be biting our fingernails until then. I just know that it will be successful, though, and I'm especially excited about seeing that first picture. You see, I first got interested in space as a teen-ager, when I saw the pictures sent back from Mars by the Viking lander. Now, just like the first picture from Viking on Mars was of its very own foot -- you could even see a footprint in the dust where the lander had apparently bounced once! -- these first pictures from Pathfinder will be of its own open side petals. For me, it will be like coming full-circle; years after marveling at those first pictures from Mars, I'll be seeing Mars again -- but through the eye of a spacecraft that I helped build with my own hands. I can't wait."
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